It is known that medication can be absorbed into the body through the soft mucosal tissues in the interior layers of the body. The medication can pass through the tissues directly into the systemic circulation, bypassing breakdown by digestive enzymes in the stomach and preventing the medication from passing through the liver where it can be degraded or eliminated. Many medications, especially proteins and peptides, are rendered useless by the gut and liver. Transmucosal delivery preserves the potency of these medications. The efficacy of transmucosal delivery depends in large part on the extent of the mucosal surface exposed to medication and the time over which the medication remains present and available on the mucosal surface.
Many medications that are administered parenterally (by injection), can also be given transmucosally. Transmucosal delivery is preferable in that close medical supervision is not required and it is not associated with scar formation, infection, and noncompliance. However, transmucosal administration is less efficient than parenteral (injectable) medication with a smaller percentage of medication entering the systemic circulation. Therefore, transmucosal administration may require a higher concentration of medication or a longer duration of administration than parenteral. Parenteral administration can produce an effect more rapidly and in a more controlled manner. However, some medications can produce unexpected, toxic effects. If toxic effects are noted shortly after parenteral injection, increasing toxicity is inevitable as the medication cannot be withdrawn. Transmucosal delivery is safer in that the medication can quickly and easily be withdrawn when signs of toxicity are noted.
Transmucosal delivery is especially suitable for pre-operative patients who must have an empty stomach; cancer patients undergoing chemotherapy or radiotherapy who are nauseated; patients who fear needles; patients with skin conditions; and children who resist swallowing or who are afraid of injections.
Transmucosal delivery forms and devices are known to the art. Medication can be delivered transmucosally through lungs, mouth, nose, vagina, conjunctiva, rectum, bladder, and urethra. Pulmonary mucosa demonstrate the highest absorption rate due to the extensive surface area of the alveolae. After pulmonary mucosa, nasal and buccal mucosa are the most penetrable, followed by rectal, and vaginal, in that order.
Oral mucosal delivery offers several distinct advantages over other routes. The mouth is easily accessible with a wide aperture and a broad mucosal surface. The medication can pass easily into the reticulated veins that lie under the oral mucosa. The oral mucosa has more lipophillic cells than other mucosae, allowing for the delivery of lipophillic medications. Medication is more easily absorbed through the oral mucosa than through skin or rectal mucosa. Medication placed in the mouth is more acceptable to patients and more easily controlled than medication placed in the rectum, urethra, vagina, bladder, or up the nose. Problems associated with oral transmucosal delivery include medication's noxious taste or irritation and the fact that a large amount of saliva (up to 2 liters per day) is produced by salivary glands in the mouth. Too much saliva can dilute and carry away medication.
Absorption rates across mucosal surfaces vary according to the physicochemical properties of the mucosa such as thickness of the epithelial layers, electrical resistance, and hydrophilic or lipophilic characteristics. Oral mucosa are generally lipophilic in nature so that molecules that are more lipophilic will penetrate more rapidly. Absorption through the mucosa is influenced by molecular size, concentration, ionization, and pH of the medication. Small, lipid-soluble molecules pass easily through the oral mucosa. Absorption is affected by the presence of various enzymes in the saliva, rate of saliva flow, viscosity, pH, and electrical resistance. It is found that medication absorbed through the buccal mucosa enters the circulation 4 to 8 times more rapidly than when it is ingested in pill or capsule form. Effects can be observed in 5-20 minutes compared to 30-60 minutes by ingestion into the stomach. Oral transmucosal delivery is also 20-30 times faster than transdermal (skin patch) delivery.